Measuring and testing – Fluid pressure gauge – Photoelectric
Reexamination Certificate
2000-03-01
2001-11-13
Oen, William (Department: 2855)
Measuring and testing
Fluid pressure gauge
Photoelectric
Reexamination Certificate
active
06314814
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to fly height performance testing, and more particularly to a method and apparatus for precise measurement of pressure dependence of head fly height using transitional thermal signals.
2. Description of Related Art
Storage capacity governs the amount of data a user can store on a computer. Adding storage capacity without increasing size means denser radial spacing of tracks on disk drives. As a result, the read/write head element's magnetic sensitivity must also increase, which makes the manufacturing process even more demanding and acceptance testing more critical.
Conventional magnetic storage devices include a magnetic transducer or “head” suspended in close proximity to a recording medium, e.g., a magnetic disk having a plurality of concentric tracks. The transducer is supported by an air bearing slider mounted to a flexible suspension. The suspension, in turn, is attached to a positioning actuator. During normal operation, relative motion is provided between the head and the recording medium as the actuator dynamically positions the head over a desired track. The relative movement provides an air flow along the surface of the slider facing the medium, creating a lifting force. The lifting force us counterbalanced by a predetermined suspension load so that the slider is supported on a cushion of air. Air flow enters the leading edge of the slider and exits from the trailing end. The head resides toward the trailing end, which tends to fly closer to the recording surface than the leading edge.
The recording medium holds information encoded in the form of magnetic transitions. The information capacity, or areal density, of the medium is determined by the transducer's ability to sense and write distinguishable transitions. An important factor affecting areal density is the distance between the transducer and the recording surface, referred to as the fly height. It is desirable to fly the transducer very close to the medium to enhance transition detection. Some fly height stability is achieved with proper suspension loading and by shaping the air bearing slider surface (ABS) for desirable aerodynamic characteristics.
Another important factor affecting fly height is the slider's resistance to changing conditions. An air bearing slider is subjected to a variety of changing external conditions during normal operation. Changing conditions affecting fly height include, for example, change in the relative air speed and direction, pressure changes and variations in temperature. If the transducer fly height does not stay constant during changing conditions, data transfer between the transducer and the recording medium may be adversely affected. Fly height is further affected by physical characteristics of the slider such as the shape of the ABS. Careful rail shaping, for example, will provide some resistance to changes in air flow. To insure compliance with such design criteria the recording heads are typically tested in an apparatus commonly referred to as a fly height tester.
Head fly height in a disk drive is dependent on the attitude at which the drive is functioning for a variety of slider air bearing designs. The head usually flies lower at higher attitude, i.e. lower pressure. Accurate measurement of head fly height vs. pressure is of importance for air bearing and file design optimization as well as for further understanding of head flying dynamics mechanism. However, the sensitivities of fly height testers have not provided accuracy at the sub-nanometer (nm) level, which is required to verify the compliance of today's head. Moreover, the pressure dependence of head fly height has not been measurable.
It can be seen that there is a need for a method and apparatus for precise measurement of pressure dependence of head fly height.
SUMMARY OF THE INVENTION
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a method and apparatus for precise measurement of pressure dependence of head fly height using transitional thermal signals.
The present invention solves the above-described problems by positioning a slider relative to a rotating disk having at least one laser bump. Calibration data is gathered by decreasing the pressure and measuring the fly height until a contact positive TA signal is detected. A non-contact negative TA signal is then normalized using the gathered calibration data. The TA signal amplitude may then be used to ascertain the fly height and pressure for a head.
A method in accordance with the principles of the present invention includes positioning a slider over a rotating disk having at least one laser bump, gathering calibration data by decreasing the pressure and measuring the fly height until a contact positive TA signal is detected, normalizing a non-contact negative TA signal using the gathered calibration data and determining a fly height and pressure for a head using the normalized non-contact thermal asperity signal.
Other embodiments of a method in accordance with the principles of the invention may include alternative or optional additional aspects. One such aspect of the present invention is that the at least one laser bump comprises three laser bumps.
Another aspect of the present invention is that the normalized non-contact thermal asperity signal provides fly height measurements with sub-nanometer sensitivity.
Another aspect of the present invention is that the determining the fly height of a head comprises detecting when the head contacts a laser bump of a known height.
Another aspect of the present invention is that the detecting when the head contacts a laser bump comprises observing when a positive contact thermal asperity signal is produced.
In another embodiment of the present invention a system for precisely measuring pressure dependence of head fly height using transitional thermal signals includes an environmental chamber for controlling the pressure therein and a spin stand, disposed within the environment chamber, the spin stand providing a disk having a plurality of laser bumps thereon with known bump heights and dimensions for interaction with a head, the spin stand further including a processor for decreasing the pressure within the environmental chamber and measuring the fly height at a plurality of pressures until a contact positive thermal asperity signal is detected, wherein the processor normalizes a non-contact thermal asperity signal using the fly height and corresponding pressure measurements and wherein the processor uses the normalized non-contact thermal asperity signal to determine the fly height and pressure for a head.
In another embodiment of the present invention an article of manufacture includes a program storage medium readable by a computer, the medium tangibly embodying one or more programs of instructions executable by the computer to precisely measure pressure dependence of head fly height using transitional thermal signals, the method including positioning a slider over a rotating disk having at least one laser bump, gathering calibration data by decreasing the pressure and measuring the fly height until a contact positive TA signal is detected, normalizing a non-contact negative TA signal using the gathered calibration data; and determining a fly height and pressure for a head using the normalized non-contact thermal asperity signal.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there are illustrated and described specific examples of an apparatus in accordance with the invention.
REFE
Brannon James Hammond
Duan Shanlin
Leung Wai Cheung
Liu Yan
Tang Li
Altera Law Group LLC
International Business Machines - Corporation
Oen William
LandOfFree
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